1. Field of the Invention
Embodiments of the present invention relate to telecommunications systems. More particularly, embodiments of the present invention relate to systems and methods for wireless telecommunications.
2. Background of the Invention
It is know that when attempting to co-locate multiple antennas, such a cellular telephone antennas, radio frequency problems are often encountered. For example, receiver sensitivity may be degraded due to a transmission signal from an adjacent transmitting antenna migrating into a nearby receiving antenna, and thereby causing internal spurious inter-modulation products to be generated. When a nearby transmitting signal migrates into another transmitting signal, “backward modulation” products can be retransmitted and can cause interference to reception of weaker signals on the same frequency. Additional problems impacting receiver sensitivity arise when the broadband noise of a transmitting signal falls within the pass band of a nearby receiver, or when the ultimate selectivity of a receiver is degraded by the reception of a nearby transmitting antenna. Another problem that exists is the inability to reuse frequencies in a typical wireless local area network such as one in accordance with IEEE 802.11 specifications. If a typical wireless node operates on a segment of available spectrum, in order to reuse the same spectrum at the same time, the energy from each node must not interfere with one another. This can be accomplished by having separate nodes with co-located low side and back lobe antennas pointing in unique directions.
Conditions may not always be conducive for degradation to occur. As an example, if in a digital system, such as GSM, the transmitting time slot of a cell phone does not occur in the same receiving time slot of a nearby cell phone, or if the cell phones are in a moderate signal strength area whereby the transmitting power output is reduced and the received signal strengths are high, there may not be any apparent degradation.
However, as the number of co-located antennas (e.g., for cell phones) increases, the likelihood of degradation increases, because there is a greater chance that time slot selection will not be optimum, such that the transmitting time slots of one cell phone will occur during the same time as a nearby receiving cell phone's time slots. If a system's use is not limited to high signal strength locations within a cellular coverage area, degradation will be more likely to occur. As an example, if the system is located in an area further from a cell site, the cell phone will transmit with high power, while the receive signal strength will be low. Under these conditions, receiver sensitivity degradation or spurious signals generation may prevent communications.
While there are arrangements for more effectively co-locating multiple cell phones, each has disadvantages. For standard cell phones or cell phone modules operating in accordance with a GSM-type system, there is a single antenna port that is switched between transmit and receive. In this type of system, co-locating cell phones through the use of passive combiners is possible, but may not provide the isolation needed to operate degradation free, and can create greater than 3 dB loss every time the number of cell phones is doubled.
If diplexers are used to separate a common receive antenna from individual transmitter antennas and filter the transmitters broad-band noise, backward transmitter inter-modulation problem will still occur in a typical installation. This partial solution is costly in terms of price and transmit signal loss.
In view of the foregoing, it can be appreciated that a substantial need exists for systems and methods that can advantageously provide for improved wireless telecommunications.